Thanks Jonathan, not sure what caused the issue at 4:34, but I can see that at 4:50 it is essential to have pressed ‘extrude region’ beforehand, (even if you just right click and don’t actually extrude). I just presumed that you could just go to ‘scale’ after selecting the faces and just scale the central portion, but I can see now this is not so. I had also not noticed before that even in the video you are scaling the central block in all directions. I can see that to retain clean 90 deg angles you need to scale down in X, then Y.
